This invention relates to a control system that responds to rainfall for such purposes as sounding an alarm, closing windows, turning off a sprinkler system etc. More particularly, the invention relates to such a control system of the general type disclosed in the Marquard, U.S. Pat. No. b 2,443,687, the Davis, U.S. Pat. No. 2,640,958 and Kaiser et al, U.S. Pat. No. 2,856,476.
Broadly described a control system of this general type has a small well which falling rain fills and has a control circuit that responds to the presence of the collected water in the well. Each of the above three patented control systems operates well in theory but in practice each of the control systems is seriously defective.
The Marquard disclosure employs a control switch which is urged to closed position by the force of a spring but is normally held open by an interposed water-soluble wafer. When water enters the small collecting well, the wafer disintegrates to permit the switch to close and energizes an alarm circuit. One serious disadvantage of this arrangement is the necessity of installing a new wafer to reset the control system. Another disadvantage is that the alarm continues to be energized for an indefinite period of time after the rain ceases. A third disadvantage is that repeated exposure of the switch contacts to rainwater causes the contacts to corrode to shorten the service life of the switch.
In the Davis disclosure, an elongated hollow float in a cylindrical well rises to electrically bridge a gap between two switch contacts to close a control circuit in response to rainfall. The lower end of the float is pointed to close a small diameter drain hole at the bottom of the well when no rainwater is in the well. When the rain ceases the well drains to lower the float. To enlarge the drain hole to prevent clogging would make the control system responsive only to a heavy rain and thus defeat the purpose of the control system.
Here again, the switch contacts are repeatedly flooded to build up corrosion. Another serious defect is that the small drain hole in the bottom of the well tends to become clogged with foreign material to make the system inoperative. A further difficulty is that the copper-clad cylindrical float tends to corrode and may stick at the lower drain hole instead of rising. It is also to be noted that the control system is used to raise the top on an automobile in the event of a rainstorm but after the rain ceases the control system does not lower the top to its original position.
In the Kaiser el al disclosure, a small rain-collecting well is mounted on a leaf spring that serves as a switch arm. The weight of the collected water in the well depresses the switch arm to energize an electric alarm circuit. The small well is occupied by a sponge or other-absorbent material which facilitates evaporation of the water in the well when the rainfall ceases.
Here again, repeated flooding of the switch contact induces corrosion that in time makes the control system inoperative. Another difficulty is that the repeated flooding of the absorbent material encourages the growth of fungus that may eventually make the alarm system defective.